A segmented mould chiefly comprises two lateral shells each of which moulds one of the lateral sidewalls of the tire, and a plurality of segments that mould the rolling of the said tire and that are radially mobile between a mould open and a mould closed position. The shells and the segments define an interior space intended to be brought into contact with the non-vulcanized green tire.
In order to mould the tread of the tire, the segments of the mould comprise lining elements. What is meant by a “lining element” is a part of the mould which comprises a moulding surface that allows at least part of the tread surface of this tread to be moulded.
It is possible to create a lining element by a powder-based additive manufacturing method by sintering or melting particles of the said powder using a beam of energy. What is meant by a “beam of energy” is an electromagnetic radiation (for example a laser beam) or a beam of particles (for example an electron beam).
The benefit of manufacturing using selective melting of superposed layers of powder, more commonly referred to as sintering, lies chiefly in the fact that the shape of these lining elements can be computer-modelled and that the lining elements can then be manufactured on the basis of this modelling by having the computer direct the beam of energy. When the selective melting is performed using a laser beam, it is called laser sintering. The laser sintering technique consists in manufacturing the component layer after layer, stacking the layers of powder which are consolidated and melted one after another by the laser beam in a direction of stacking.
Patent application WO-A1-2012/156439 describes a particular lining element obtained in part using this laser sintering technique. The lining element is made up of a sintered moulding part for moulding the tread of the tire, and of a non-sintered support base secured to the moulding part and forming an interface with the associated mould. The sintered moulding part comprises bars and sipe blades for forming the tire tread patterns.
In a way known per se, the patterns of the tread of the tire play a key role in the grip of this tire, chiefly when driving on wet and/or snowy ground.
In order to maintain over the course of time a tire that has good grip and water-drainage performance, it is known practice to provide, for the tread of the tire, tread patterns that evolve with tire wear. To do that, cavities are formed beneath the tread surface of the tread when the tire is new and are intended after partial wear to form a new tread pattern the characteristics of which are tailored to suit the reduced thickness of the tread. For further details regarding such evolving tread patterns, reference may for example be made to patent application FR-A1-2 763 892.
In that anterior document, in order to succeed in moulding cavities beneath the tread surface of the tread, the associated curing mould comprises a plurality of fingers attached to each lateral shell and projecting with respect to the moulding surface of the said shell.
In order to be able to demould the tire, it is necessary to produce each lateral shell in two parts and to provide between these means of connection that allow the part supporting the fingers to rotate with respect to the other part. This appreciably increases the cost of manufacture of the mould. Furthermore, the fixing of the fingers to the lateral shells does not allow cavities to be moulded into all the desired regions of the tire tread.
An alternative solution for succeeding in moulding tread patterns that evolve according to the degree of tire wear is to fix to the segments of the associated curing mould sipe blades which are shaped in such a way as to obtain tear-drop shaped cuts in the tire tread. FIG. 6 of document FR-A1-2 961 741 discloses such a sipe blade which is obtained by laser sintering. Specifically, this technique is well suited to the manufacture of small-sized elements of complex shapes, such as these sipe blades, which are difficult to manufacture by other methods.
However, in order to obtain cuts of the teardrop type, such sipe blades comprise a main body of relatively small cross section. The sipe blades may suffer deformations and/or damage during the course of manufacture that may cause stress concentrations and micro cracks to appear.